This invention relates generally to lasers, and, more particularly, to an internal arresting beam clipper utilized primarily with a laser in order to remove high intensity, high power portions from out-of-round laser beams and thereby minimize on-target intensity losses due to aperture diffraction.
Lasers are now well established in the art for generating coherent electromagnetic radiation in the optical frequency range. The operation of a laser is based upon the fact that the atomic systems represented by the atoms of the laser material can exist in any of a series of discrete energy level or states, the systems absorbing energy in the optical frequency range in going to a higher state and emitting it when going to a lower state. In the case of ruby as a laser material, three energy levels are utilized. The atomic systems are raised from the lower or ground level to the higher of the three levels by irradiation from a strong light source which need not be coherent but should preferably have a high concentration of energy in the absorbing wavelengths. A radiationless transition then occurs from the highest state to an intermediate or metastable state. This is followed by a transition with photon emission from the intermediate state back to the ground state. It is the last transition that is of interest since this transition is the source of the coherent light or electromagnetic energy produced by the laser.
The operation of raising the energy level of the laser material to produce the desired photon emission is referred to in the art as "pumping" and when more atoms reach an excited metastable state than remain in a lower energy level, a "population inversion" is said to exist.
The active material in the laser is made optically resonant by placing reflectors at either end thereof to form a resonant cavity. The reflector on at least one end is made partially transmissive or is in the form of a pair of reflectors so that there will be an escape from the resonant cavity of a laser beam.
Gas lasers are generally made up of an elongated hollow tube sealed at both ends thereof by a pair of laser windows and filled with any suitable laser reactant mixture. Adjacent the sealing windows are situated the reflective surfaces, forming therebetween the resonant cavity. The lasing action takes place as a result of, for example, a suitable chemical reaction or electron beam excitation.
Generally, in smaller dimensional lasers in which the resonant cavity is of a rectangular cross-sectional configuration, the beam emanating therefrom is out-of-round. In such lasers it is necessary to clip the high intensity, high power portions of the out-of-round laser beam in order to substantially reduce on-target losses due to aperture diffraction.
Previous clipping systems have involved the passing of laser beams through angled mirrors with large central holes. The beam to be projected to the target passes through the center hole while the unwanted corners of the beam are clipped by the surrounding mirror and deflected to a remote absorber. The absorber surface consists of sharply angled facets with highly absorbing surface coatings; these are intended to achieve complete absorption while limiting local Q/A (i.e., beam flux per area or abosrbed heat flux) by presenting shallow angles of incidence to the radiation being absorbed. Such an approach represents the general prior art philosophy of clipping and is similar to related calorimeter approaches.
The systems of the past left much to be desired since the requirements for remote absorbers brought about the associated problems of propagation volume and optical aiming associated with the remote absorption. In addition, calorimeter-type converging wedge absorbers produced high heat-flux knife edges, the need for double wall construction and cumbersome design. Clearly a need exists in laser technology for a simplified, reliable and more efficient system of beam clipping than has heretofore been available.